1. Field of the Invention
The present invention relates to an optical mouse and, more particularly, to a method of calculating sub-pixel movement and a position tracking sensor using the same in which resolution to the movement of an optical mouse can be enhanced when the optical mouse moves precisely.
2. Description of the Related Art
In general, as shown in FIG. 1, an optical mouse includes a light source 1 that generates and emits light 2; a lens 4 that gathers reflected light when the light 2 emitted from the light source 1 is reflected from a surface 3 of a worktable, and a position tracking sensor 6 that detects movement from an image change of the surface illuminated by light 5 incident through the lens 4 and calculates a movement value.
With this configuration, the position tracking sensor 6 extracts and stores a surface image at a very high speed. Each image extracted and stored in this way is referred to as a “frame.” The position tracking sensor 6 calculates correlation between the stored frames to recognize the movement of the optical mouse and outputs a value corresponding to the movement.
FIG. 2 is a diagram illustrating a frame configuration method of the position tracking sensor shown in FIG. 1 and a method of calculating sub-pixel movement using the same.
As shown in FIG. 2, the position tracking sensor requires a reference frame and a sample frame to calculate the movement value of the optical mouse.
Here, the sample frame is a current image extracted and stored by the position tracking sensor, and the reference frame is one that the previous sample frame is stored.
Thus, the position tracking sensor sets a reference area in a single entire frame selected and stored as the reference frame, and calculates correlation between the currently inputted sample frame and the reference area while scanning every pixel by a pixel unit in a zigzag direction from an upper left end to a lower right end of the sample frame, and finds the location of the sample frame whose correlation is the highest to calculate a moving direction and a moving distance.
When the highest correlation is found by comparing the sample frame with the reference frame, if the sample frame moves from at least 0.5 pixel to at most 1.5 pixels with respect to the reference frame, it is calculated that the sample frame moves by one pixel, and if the sample frame moves more than a preset value with respect to the reference frame, the reference frame is updated to the current sample frame, and then the updated reference frame is used as the reference frame when the next sampling is carried out.
The following Table 1 represents the number of times recognizing movement of the optical mouse according to operation of the position tracking sensor of FIG. 2.
TABLE 1Sampling No.NN + 1N + 2N + 3N + 4N + 5N + 6N + 7N + 8Actual moving distance (pixel unit)0.00.40.81.21.62.02.42.83.2Update of reference frameYes————————Distance between reference frame and0.00.40.81.21.62.02.42.83.2sample frameRecognition of movement of sample——Yes—Yes——Yes—frame with respect to reference frame?Number of times recognizing0  0  1  1  2  2  2  3  3  movement of sample frame withrespect to reference frame
As shown in Table 1, the movement of the sample frame with respect to the reference frame of the position tracking sensor is first recognized when the sample frame moves at a distance of at least about 0.5 pixel at the time when the reference frame is updated, and then is additionally recognized whenever the moving distance is increased by about 1.0 pixel.
In other words, when the number of the reference frame is one (1), the position tracking sensor recognizes the movement of the optical mouse, whenever the moving distance is increased from about 0.5 pixel to about 1.5 pixels, from about 1.5 pixels to about 2.5 pixels, etc.
Therefore, the optical mouse having one reference frame recognizes the movement at the time point of N+2 when the actual moving distance amounts to 0.8 pixel, and further recognizes the movement at the time point of N+4 when the actual moving distance amounts to 1.6 pixels.
However, in the above-mentioned method of calculating sub-pixel movement of the position tracking sensor, the movement is recognized by 0.5 pixel unit, only when the movement of the optical mouse is first recognized after the position tracking sensor updates the reference frame, and then the movement of the optical mouse is not additionally recognized until the optical mouse moves above one pixel.
Therefore, the position tracking sensor cannot recognize the movement of below 1.0 pixel, i.e. sub-pixel, so that it has a problem that resolution is degraded.